JIAJIA and MPI (message passing interface) are compared in this paper. JIAJIA and MPI represent the programming model of share memory and message passing respectively. MPI handles message transmission manually and is hard for programming. JIAJIA maintains data coherence by lower layer and provides simple message passing APIs, so it is easy and flexible to program. It takes more time for JIAJIA to initialize applications than MPI. A rough empirical formula about speedup and machine size is presented in this paper. Experimental results show that both JIAJIA and MPI have good parallel performance on PC clusters and their performance difference of most testing applications is lower than 10 percent. Applications with fewer messages have better performance and the gap between JIAJIA and MPI is minor. While messages increase, parallel performance decreases and the gap between JIAJIA and MPI depends on the amount of messages they produce.